The Digital Subscriber Line (DSL) technology is a high speed transmission technology that performs data transmission through telephone twist pair line, i.e., Unshielded Twist Pair (UTP), including Asymmetrical Digital Subscriber Line (ADSL), Very-high-bit-rate Digital Subscriber Line (VDSL), Digital Subscriber Line based on Integrated Services Digital Network (ISDN) (ISDN Digital Subscriber Line, IDSL) and Single-pair High-bit-rate Digital Subscriber Line (SHDSL), etc.
With the improvements of the frequency bands used by various DSL technologies (xDSL), more and more problems of cross-talk, especially cross-talk in high frequency bands, pop out. The uplink and downlink channels of the xDSL use Frequency Division Multiplexing (FDM), and the influence from the Near-End Cross-Talk (NEXT) can be greatly reduced through the filter, thus the system performance will not be damaged too much; but due to the frequency band of the Far-End Cross-Talk (FEXT) and the received signal in the system being within the same frequency band, the transmission performance of the system will be seriously affected. When multiple channels of subscribers in a bundle of cables all require activating xDSL service, some lines will have low rates, unstable performances and even cannot be conducted due to the FEXT, and finally, the line activation rate of the DSL Access Multiplexer (DSLAM) is low.
The conventional art uses a Dynamic Spectrum Management (DSM) technology to reduce the influence of cross-talk. The DSM technology reduces the cross-talk by automatically adjusting transmission power on each line of the network. FIG. 1 is a conventional network reference model for implementing the DSM.
In the conventional art, the following equation is generally optimized by Optimum Spectrum Balancing (OSB), Iterative Spectrum Balancing (ISB) and Iterative Water-Filling (IWF), so as to maximize a sum of weighted rates of all subscribers by adjusting the transmission power value of all subscribers on each subcarrier respectively, under the condition that the total transmission power of each subscriber does not exceed a threshold.
      max    ⁢                  ∑                  n          =          1                N            ⁢                        ω          n                ⁢                              ∑                          k              =              1                        K                    ⁢                      b            k            n                                -            ∑              n        =        1            N        ⁢          λ      ⁢                        ∑                      k            =            1                    K                ⁢                  S          k          n                    
Wherein, skn is transmission power of the nth subscriber at the kth subcarrier; Pn is a threshold of total power of the nth subscriber; ωn is a rate weight coefficient of the nth subscriber; λ is a Lagrange multiplier; N is a total number of the subscribers; and K is a total number of the frequency points.
During the process of implementing the present invention, the inventor finds that the conventional art has the following defects: in the current DSM Level 2 technology, most algorithms need to search the rate weight coefficient ωn. But the variation range of the rate weight coefficient may be very extensive and is difficult to converge, sometimes a slightly variation of the rate weight coefficient may cause the rate to increase or decrease for a large extent, therefore it is difficult to search the rate weight coefficient, thus there exists a certain difficulty in optimizing the rate to a target rate with the above algorithms.